It is well known to provide protection devices, such as motor protectors, for electromotive compressor motors employed in air conditioners and the like (hereafter also referred to as motor protection device). The motor protection device typically includes movable contacts controlled by a current carrying bimetal element which is actuated by elevated environmental temperatures and/or overcurrents. The motor protection device is typically attached to a motor coil of the compressor motor mounted inside the casing of the electromotive compressor. The motor is connected to an external alternating current power source through the motor protection device, lead wires and glass sealed terminals provided in the casing.
If the electromotive compressor is subjected to an overload or a locked rotor condition due to abnormal circumstances, the environmental temperature inside the casing rises and/or the amount of electric current that passes through the motor protection device rises, the motor protection device then opens the power source circuit by actuation of the bimetal element, thereby preventing possible damage in the compressor caused by excessive temperature or overcurrent. When the temperature and current value are restored to the normal state, the motor protection device closes the power circuit once again and restores the power supply to the compressor.
However, if the motor protection device has been used beyond its useful product life, its contacts could weld together with a result that there are cases where an electrically conductive state continues to be maintained even when the electromotive compressor happens to be in a fault condition. In such cases, the temperature of the motor winding rises further and the electrically insulating material on the winding conductors melts, thereby causing short-circuiting between the windings or the glass of the glass seal melts, with the terminal being blown out by the internal pressure in the sealed casing.